Surface-treated silica



- acter.

Patented Dec. 11, 1953 SURFACE-TREATED SILICA Daniel S. Sears, CuyahogaFalls, and Edwin B.

Newton, Akron,

hio, assignors to The B. F.

Goodrich Company, New York, N. Y., a corporation of New York No Drawing.Application November 1, 1947,

Serial No. 783,628

9 Claims. (01. zoo-use) This invention relates to surface-treatedsilicon dioxide for use in rubber compounding and is particularlyconcerned with finely-divided silicon dioxide which is the solid productof combustion of silicon-bearing material, the silicon combustionproduct having basic material disposed on the surface thereof wherebythe treated silica is adapted for use in combination with a rubber in avulcanizable composition.

Silica prepared by the combustion of siliconbearing material isparticularly suitable for use as a reinforcing material in rubbercompositions least substantially equivalent to the acidic equivalent ofthe combustion silica.

Silica prepared in other ways than by the combustion of silicon-bearingmaterial has little or no reinforcing effect on rubber regardless of theacidic or basic condition of the composition. Combustion silica has truereinforcing properties only under the proper condition of basicityduring vulcanization of a composition including combustion silica. Itis, therefore, an object of this invention to provide a composition ofmatter suitable for incorporation into conventional vulcanizable rubbercompositions to obtain maximum reinforcement of the rubber compositionupon vulcanization. Other objects will be apparent from the descriptionwhich follows.

A composition of matter embodying this invention comprisesfinely-divided silicon dioxide which is the solid product of combustion,of

- silicon-bearing material, together with basic material adsorbed on thesurface of the particles of the silica in an amount suflicient at leastto substantially offset the normal surface acidity of the purposes ofbrevity, exhibits an anomalous char- F'or example, the product preparedby burning silicon-bearing material in the presence of oxygen consistssubstantially of pure silicon dioxide and has a marked degree of surfaceacidity which is not due to free acid adsorbed on the surface. Thisacidity appears to be due to groups of acid character on the surface,the

:nature of such acidic groups, if such they are, not

being understood. The material normally exhibits surface acidity, butthe surface acid cannot be leached away with water indicating that theacid components are integrally bound in the particle surface.

Unlike 'channel black, which also exhibits an acidic character,untreated combustion silica cannot be successfully employed inconventional rubber compounding recipes; but, as disclosed in ourcopending application, basic materials mustbe present duringvulcanization. A composition of matter embodying this invention,however, may be incorporated directly into a vulcanizable compositioncomprising a vulcanizable rubber and vulcanizing agent therefor, and theresulting composition subjected to vulcanization in the usual manner.

The combustion silica which is used in practising this invention is theamorphous material having a particle size of 5-200 millimicrons preparedby the combustion of a silicon-bearing material, and preferably theproduct of combustion in the presence of sufficient oxygen to yieldsubstantially pure silicon dioxide, although the combustion may be in anatmosphere of nitrogen to form a nitride and the combustion silica mayin-- clude any amorphous solid combustion product of silicon-bearingmaterial. It may be prepared by combustion of any of the normally solid,liquid, or gaseous silicon-bearing materials. For example, normallysolid materials'such as silicon metal, ferrosilicon, silicon nitride,silicon monosulfide, silicon tetra-acetate, silicon disulfide, etc., maybe vaporized in a furnace or electric arc and rapidly oxidized to' afinely-divided silica smoke. Alternatively, such solid materials may bepowdered and sprayed into an oxygen-gas flame, whereupon the particlesignite and form the desired silica. A particularly suitable method ofpreparing combustion silica from solid materials such as sand,ferrosilicon, etc., is to mix the silicon-bearing material with groundcoal or similar powdered carbon fuels and burn the mixture in a furnacein the presence of sufficient air to convert all of the silicon tofinelydivided silicon dioxide.

silicon tetrachloride, silicon hydride, trisilican'e amine, bromosilicane, dibromo silicane, dichloro silicane, silicane ether, tribromosilicane, trichloro silicane, trifiuoro silicane, triiodo silicane,silicon tetrabromide, silicon bromo trichloride, silicon dibromodichloride, silicon tribromo chloride, chlorosilicane, silicon chloro.hydrosulfide, silicon tetrafluoride, disilicane, trisilicane,tetrasilicane, silicon iodo trichloride, silicon oxychloride,disiloxane, dimethyl silicane, ethoxy triethyl silicane, methylsilicane, tetraethyl silicane, tetramethyl silicane, trichlorophenylsilicane, triethyl silicane, chloromethyl silicane, dichloromethylsilicane and similar materials. Thus, any silicon dioxide which is thefinelydivided amorphous product of combustion of a silicon-bearingmaterial may be used within the scope of this invention, all suchmaterials normally exhibiting the surface acidity characteristic ofcombustion silica.

Any basic material may be adsorbed on the surface of the combustionsilica in preparing a composition of matter embodying this invention.Thus, the silica may be surface treated with any free base, whether aninorganic base such as sodium, potassium, or ammonium hydroxide or anorganic base such as an amine. f the organicbases, the substitutedamines such as triethanolamine or the quaternary ammonium bases such astetramethyl ammonium hydroxide may be used. The amines preferablyemployed, however, are those in which the amine is joined to ahydrocarbon structure; including any of the primary, secondary, ortertiary amino roups joined to either saturated or unsaturated aliphatichydrocarbon structures or to an aromatic structure or both. Thus, forexample, suitable amines include diallyl amine, diamyl amine, dibenzylamine, dibutyl amine, dicyclohexyl amine, ethyl amine, diethyl amine,ethylene diamine, tertiary butyl amine, alpha-phenyl ethyl amine,phenethyl amine, methyl amine, hexamethylene tetramine, diphenylguanidine, diorthotolyl guanidine, triphenyl amine, tripropyl amine,trimethylene diamine, isohexyl amine, secondary butyl amine, aniline,diphenyl amine, alphanaphthyl amine, beta-naphthyl amine, phenylbeta-naphthyl amine and similar well known amines.

Particularly desirable amines for use in practising this invention arethe long-chain aliphatic amines, i. e., those having at least 8 carbonatoms in the aliphatic chain, such amines aiding materially indispersing silica coated with the amine in rubber. Such amines aretypified by dodecylamine, dilaurylamine, octylamine, hendecylamine,dioctadecylamine and similar aliphatic amines.

The amount of basic material to be used in combination with a givenweight of combustion silica must be suflicient to offset the apparentacidity of the silica, with excess basic material preferably beingpresent. For practical purposes, the amount of basic material employedin the compositionis from 0.1 to milliequivalents of base per mole ofcombustion silica with 1 to 5 milliequivaients of base per mole ofcombustion silica being preferably used. In the case of a normally acidvulcanizable composition, an excess of basic material in the siliconmaterial over the amount required to neutralize the acidity of thesilicon material serves to react with the free acid in the compositionto facilitate vulcanization; and, in such a case, the composition ofmatter may include the maximum amount of base which can be adsorbed bythe combustion silica, that is, about 25 milliequivalents of base permole of combustion silica.

The combustion silica may be surface treated with the basic materials inany desired manner. In the case of readily volatilized bases, such asethylene diamine, the silica may be contacted with vapors of the base toattain the desired adsorption. Alternatively, the base may be dissolvedin a suitable volatile solvent and the silica treated with the solution,after which the volatile solvent is removed by evaporation. Normallyliquid bases may be sprayed on the silica as a flne mist. Any of thecommon and well known expedients for surface-treating solid particulatematerials may be employed in addition to the methods enumerated.

A few typical examples of the combustion silica-base compositions willbe set forth for purposes of illustration as well as a few typicalexamples of vulcanizable composition including surface-treated silica.It will be understood that the examples are merely illustrative and itis not intended that the scope of the invention be limited therebyExample 1 Ethyl silicate is vaporized and the vapors thereof admixedwith illuminating gas, the gaseous mixture is ignited in air and thefinely divided combustion silica is collected. This combustion silica isspread in a thin layer and the vapors of ethylene diamine are passedover the silica for 30 minutes. The composition obtained is as follows:

Material: Parts by weight Combustion silica i000 Adsorbed ethylenediamine 0.4

Total 100.4

Example 2 Fine sand and ground coal are admixed and vaporized in anelectric furnace and the vapors are burned in an oxidizing atmosphere toform combustion silica. This material is sprayed with dodecylamine whichhas been liquefied by heating to C. The following composition issuitable for rubber compounding:

Material: Parts by weight Combustion silica 100.0 Adsorbed dodecylamine1.0

Total 101.0

Example 3 Combustion silica which contains adsorbed basic material maybe used in combination with a vulcanizable composition including anyvulcanizable rubber, that is, any rubber whether natural or syntheticwhich may be heated with sulfur, sulfides or oxides to impart increasedelasticity, hardness, etc., thereto.

Thus, a conventional compounding recipe using natural rubber is asfollows:

Such a composition may be readily vulcanized 75 by heating at 280 F. forminutes using conaeraeoe ventional reinforcing material such as carbonblack. By means of this invention, surfacetreated combustion silica maybe used as the re-, inforcing material in this recipe without any changetherein. The combustion silica obtained by burning ferrosilicon istreated with dilaurylamine (5 milliequivalents of base per mole ofsilica), the resulting composition employed as the reinforcing materialin the foregoing vulcanizable composition and the resulting compositionvulcanized. The vulcanizate has a tensile strength above 4000 p. s. i.and crescent tear resistance above 60 lbs. per 0.1 inch.

Example 4 In some cases, it may be desirable to adsorb a basicvulcanization accelerator on the combustion silica. A typical example ofcombustion silica treated with a solution of diphenyl guanidine inalcohol and used in conjunction with a diene polymer is as follows:

Material: Parts by weight Butadiene-styrene copolymer (75:25

copolymer by weight) 100.0

Zinc oxide 2.0 Pine tar resin 8.0 Sulfur 3.0

Treated combustion silica (silica 40 parts; diphenyl guanidine 2.5parts) 42.5

Total 155.5

This composition is vulcanized by heating at Example 5 Similarly,combustion silica prepared by buming finely powdered silicon may betreated with a mixture of triethanolamine and triethyl trimethylenetriamine by mixing the components in a ball mill. The resultingcomposition may be used in combination witha butadiene-styrene copolymeras follows:

Material: Parts by weight Butadiene-styrene copolymer (60:40

copolymer) 100.0

Zinc oxide 5.0

Stearic acid 7.0

Sulfur 3.0

Treated silica Tamar 5.; "511565 15.5

parts; triethanolamine 3.0 parts; triamine 1.0 part) 49.0

Total 164.0

vulcanization is carried out at 260 F. for 30 minutes. The resultingcomposition has a tensile strength in excess of 3000 p. s. i. and acrescent tear resistance of 30 lbs. per 0.1 inch.

The invention has been described in considerable detail with referenceto a few preferred embodiments thereof but it will be understood thatvariations and modifications may be effected within the spirit and scopeof the invention as defined in the appended claims.

We claim:

i. A composition of matter consisting essentially of finely-dividedsilicon dioxide which is the solid product of combustion of-a silicon- 6bearing material, which silicon dioxide is normally characterized bysurfaceacidity. and an amine disposed on the surface of said silicondioxide in an amount at least sufficient to substantially neutralizesaid surface acidity.

2. A composition of matter consisting essentially of silicon dioxide ofan average particle.

diameter of 5-200 millimicrons which is the solid product of rapidoxidation of a silicon-bearing material, and an amine adsorbed on thesurface of said silicon dioxide in an amount at least sufficient tosubstantially offset the normally acid character of the surface of saidsilicon dioxide, which amine contains only carbon, hydrogen, and aminonitrogen atoms.

3. A composition of matter consisting essentially of finely-dividedsilicon dioxide which is the solid product of burning a normally solidsilicon-bearing material, and an aliphatic amine having from 8 to 36carbon atoms adsorbed on the surface of said silicon dioxide in anamount at least sufflcient to substantially neutralize the normally acidcharacter of the surface of said dioxide.

4. A composition of matter consisting essentially of particulate silicondioxide having an average particle diameter of 5-200 millimicrons whichis the solid product of combustion of a silicon-bearing material, saidsilicon dioxide having an aliphatic amine adsorbed on its surface in theproportion of 0.1 to 15 milliequivalents of base per mole of silicondioxide, which amine contains from 8 to 36 carbon atoms.

5. A composition of matter consisting essentially of finely-dividedsilicon dioxide which is the solid product of combustion of asiliconbearing material, and dodecylamin adsorbed on the surface of saidsilicon dioxide in an amount at least sufilcient to substantiallyneutralize the normally acid character of the surface of said dioxide.

6. Finely-divided amorphous silicon dioxide having an average particlediameter of 5-200 millimicrons, said silicon dioxide being the solidproduct of combustion of silicon-bearing vapors said silicon dioxidehaving adsorbed on the surface thereof dodecylamine in an amount atleast suflicient to substantially neutralize the normal surface acidityof said silicon dioxide.

7. A vulcanizable composition of matter comprising a vulcanizable rubberand vulcanizing agent therefor, and a finely-divided silicon dioxidewhich is the solid product of combustion of silicon-bearing material,said silicon dioxide having an amine adsorbed on the surface thereof inan amount at least sufficient to substantially oil'set the normalsurface acidity of said silicon dioxide, said silicon dioxide beingdispersed in said rubber and amounting to about.40 to 50% by weight ofsaid rubber. v

8. A vulcanizable composition of matter comprising a vulcanizable,rubber and vulcanizing agent therefor, and amorphous silicon dioxidehaving a particle size of 5-200 millimicrons which is the solid productof combustion of-siliconbearing vapors, said silicon dioxide beingnormally characterized by surface acidity and having adsorbed on thesurface thereof in an amount at least sufficient to neutralize the acidat the surface of the silicon dioxide particles an allphatic aminecontaining from 8 to 36 carbon atoms, said silicon dioxide beingdispersed in said rubber and amounting to about 40 to 50% by weight ofsaid rubber.

9. The method of making a reinforcing pig- 7 8 meat suitable for use ina vulcaniable rubber composition which comprises adsorbing on theREFERENCES ITED surface Of a finely-divided 81110011 dioxide which Thefollowing references are of record m tho is the solid pricfiuctoincomgaustilgxiinoi a $111282; file or this patent: bearing mater an apha ic a e cont 5 from 8 to 36 carbon atoms. said silicon dioxide UNITEDSTATES .PATENTB being normally characterized by surface acidity, NumberName Date the amount of said basic material being at least 1,730,485Teague Oct. 8, 1929 sufllcient to substantially neutralize said surface1,843,576 McClure et a1 Feb. 2, 1932 acidity. 30 3,103,481 rsilock et a1Dec. 28, 1937 382,006 oan May 5, 1942 DANIEL SEARS 2,348,072 KanhoferMay 2, 1944,

EDWIN 2,428,252 Von Strob Sept. 30, 194-1

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF FINELY-DIVIDEDSILICON DIOXIDE WHICH IS THE SOLID PRODUCT OF COMBUSTION OF ASILICONBEARING MATERIAL, WHICH SILICON DIOXIDE IS NORMALLY CHARACTERIZEDBY SURFACE ACIDITY, AND AN AMINE DISPOSED ON THE SURFACE OF SAID SILICONDIOXIDE IN AN AMOUNT AT LEAST SUFFICIENT TO SUBSTANTIALLY NEUTRALIZESAID SURFACE ACIDITY.